A group III-V compound semiconductor such as GaN and AlGaN is widely used for optoelectronics and electronic devices due to its advantages including having a wide and easily-adjustable band-gap energy.
Particularly, light-emitting devices such as a light-emitting diode or a laser diode using a group III-V or group II-VI compound semiconductor material may implement various colors such as red, green, blue, and ultraviolet (UV) due to development of thin film growth technique and device materials, may also implement highly-efficient white light by using a fluorescent material or combining colors, and have advantages of low power consumption, semi-permanent service life, rapid response speed, safety, and eco-friendliness in comparison to conventional light sources such as a fluorescent lamp and an incandescent lamp.
Therefore, application of the light-emitting devices has been expanded to a transmission module of an optical communication means, a light-emitting diode backlight which is a substitute for a cold cathode fluorescence lamp (CCFL) constituting a backlight of a liquid crystal display (LCD) device, a white light-emitting diode lighting device capable of substituting for a fluorescent lamp or an incandescent lamp, a vehicle headlight, and a traffic light.
A light-emitting device has a light-emitting structure including a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer, and a first electrode and a second electrode are respectively disposed on the first conductive semiconductor layer and the second conductive semiconductor layer. The light-emitting device emits light, which has energy determined by a unique energy band of a material forming the active layer, by electrons injected through the first conductive semiconductor layer and holes injected through the second conductive semiconductor layer meeting each other. Light emitted from the active layer may vary in accordance with a composition of the material forming the active layer, and may be blue light, UV light, deep UV light or the like.
FIG. 1 is a view illustrating a conventional light-emitting device.
A vertical light-emitting device illustrated in FIG. 1 has a light-emitting structure (10), which includes a first conductive semiconductor layer (12), an active layer (14), and a second conductive semiconductor layer (16), disposed above a second electrode (16), and has a first electrode (13) disposed above the first conductive semiconductor layer (12).
Light extraction mostly occurs in a horizontal direction in the conventional light-emitting device. In this case, there is a problem in that, when an optical path along which light generated from the active layer (14) of the light-emitting device is extracted to the outside of the light-emitting device lengthens, absorption occurs inside the light-emitting diode, and thus light extraction efficiency is degraded.
Further, there is a problem in that light emission mostly occurs at a certain portion at which current spreading is weak, most of the emitted light is absorbed at the portion from which the light is emitted, and thus light extraction efficiency is degraded.